Downhole tools and equipment are run downhole on support members such as cables or coiled steel tubing. These support members, together with the tools or equipment that they support, are forced downhole using equipment such as an injector head.
An injector head is conventionally used to feed coiled steel tubing from surface down a hydrocarbon well. An injector head consists of a pair of opposed chains between which the coiled tubing is sandwiched. The chains are fitted with rubber blocks in an arrangement like a tank track. Each chain and rubber block arrangement is wrapped around a pair of cogs, one or both of the cogs being driven. The rubber blocks grip the coiled tubing and as the chains rotate in opposite directions about the cogs, the coiled tubing is pushed downhole.
Conventional injector heads have drawbacks however. Quite often the coiled tubing is not centred in the injector head causing one chain to apply a greater pressure than the other chain resulting in wear on one of the chains.
Additionally, chains are expensive and difficult to maintain, requiring constant lubrication with the associated potential for environmental damage. In the event of failure of the chains, significant downtime can result.